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Monday, August 31, 2015

Not too long ago, RNAi Therapeutic got dumped by Big
Pharma in a big way not least because of the monoclonal/recombinant protein
pedigree and corresponding bias among the top dogs of these organizations. This was most obvious with Roche and Merck
when changes in their overall R&D organizations led to the loss of their
last internal RNAi champions.

How times have
changed. Yesterday, The Medicines Company (who have now become a natural acquisition target) and Alnylam presented data (press release here, data here) strongly suggesting that an RNAi Therapeutic will push aside the temporally
more advanced monoclonal antibody competition to become the best-in-class agent
in the potentially top pharmaceutical category over probably the next two
decades: the inhibition of PCSK9 for the prevention of cardiovascular morbidity
and mortality.

The data in support of this claim were presented yesterday
at the 2015 ESC congress in London that in retrospect was apparently named in
honor of the delivery technology underlying ALN-PCSsc, a so-called Enhanced Stabilization Chemistry-based
RNAi conjugate.

Treatment adherence

Importantly, the single-dose part of the study showed that
starting with a dose of 300mg of ALN-PCS, PCSK9 levels were flat-lined to ~25%
of normal levels for at least 4-5 months and haven’t started to perk up yet by
the data cut-off date for this presentation.
It is to be expected that the knockdown will be even more
pronounced with repeat dosing as supported by the initial repeat-administration
data (2/3 doses) showing mean PCSK9 reductions to ~15% of normal.

Since in the PCSK9 category, it is PCSK9 that is driving
LDLc lowering, the ultimate aim of this therapeutic approach, similar kinetics
were seen in terms of LDLc levels in the blood with reductions (and
safety/tolerability profiles) comparable to that seen with the recently
approved monoclonal antibodies PRALUENT (by Regeneron/Sanofi) and REPATHA (by
Amgen), ~55-60%.

In the case of the monoclonal antibodies, dose administrations every two weeks is really what it takes
to consistently suppress PCSK9/LDLc because their inhibitory ability is
directly correlated to their amount in the blood which declines rather
precipitously after drug administration.
In the case of RNAi, however, you only need minute amounts to clamp down
gene expression and at least for the liver, it appears that
quarterly/semi-annual dosing schedules are realistic (it also depends on target and how much it needs to be repressed; e.g.
with CC5 you may need much more target gene knockdown than 58-90%).

Sticking a needle into you just 2 or 4 times a year instead
of 26 times, of course, has great advantages when it comes to treatment adherence. Keeping patients on drugs is a major issue for such life-long therapies especially since the disease is not felt acutely. This point was made repeatedly
by cardiovascular disease thought leader Dr. Kastelein on the companies’conference call. By being able to
co-ordinate drug administration with routine doctor visits, it would be
possible to achieve very high compliance rates thereby preventing intermittent LDL
cholesterol spikes that are believed to be particularly harmful.

In other words, assuming cardiovascular outcomes to be
almost entirely driven by LDLc lowering, ALN-PCSsc would/should be
best-in-class in the PCSK9 category.
There are numerous examples such as Eylea in the wet AMD space where
injection frequency is the main competitive driving force among competing agents (here VEGF inhibitors) that exemplify how being a best-in-class follower can be very profitable. Let the monoclonals build the PCSK9 market
for ALN-PCSsc to then take it.

Outcomes

Last but not least, the ultimate value from being different will come from the results of the cardiovascular outcomes
(and actually overall survival) studies that will really unleash the wide
adoption of the PCSK9 class. Due to their similarities, there is every reason to believe that the
results from the monoclonal antibodies will cluster tightly. By contrast, for better or worse, the outcome studies from ALN-PCSsc should be notably different and given that an RNAi agent mimics the compelling human genetics behind
the PCSK9 story (extreme LDLc lowering in
PCSK9-mutant individuals without other apparent untowards effects such as
elevated liver triglycerides etc) much more closely, I like my chances here.

We
all know about the intricate feedback mechanisms of lipid biology so that
binding a player merely in the serum as the monoclonals do as opposed to
removing it from both inside and outside the cell could have unanticipated
consequences. Albeit early, the
preliminary data from ALN-PCSsc support that in that the percent LDLc knockdown is
the same whether in the presence or absence of high-dose statins whereas that
of the monoclonal antibodies becomes muted.

Having said that, expect the monoclonal antibody establishment
to play the 'RNAi is different from monoclonal antibody card' lest ALN-PCS piggy-backs on the MAb CVOT results expected to come out starting in 2017.

Back to my self-imposed exile, but I couldn't resist on commenting on what could be a perfect Oligonucleotide Therapeutics storm that is building. Next up is (maybe) ARC-520 for HBV. And yes, I'm long MDCO as if that's not obvious.

Tuesday, June 23, 2015

When it feels that everything has been said, it may be time to be silent for a while.

This point has come for me and the RNAi Therapeutics blog and I look forward to take part in the conversation with renewed energy and ideas. Until then, you can follow the 'light' version of this blog on Twitter @RNAiAnalyst.

Thursday, June 11, 2015

The fairy-tale story of the splice modulation for spinal muscular atrophy (SMA) continues. This
morning, Isis Pharmaceuticals provided an update on the phase II study of
ISIS-SMNRx in type I SMA infants. The data built on already highly promising data as of last September, showing that a doubling (~9 to ~18 months)
of the median ‘event-free survival’ compared to the Natural History has now
been reached with numbers still increasing as more than half the infants remain event-free.

Only one out
of 12 infants still on study suffered an event (permanent ventilation) over the
last 9 months. This one in 108 month
event rate compares to 6 events in ~200 months in the prior phase of the
study, suggesting that if babies can be diagnosed and treated early enough so
that they are covered during a critical period of development (e.g. maturation
of the neuromuscular synapse) chances are that they will enjoy a very
significant treatment benefit from ISIS-SMNRx.

This is thus
consistent with the biomarker data showing that ISIS-SMNRx increases the
missing functional full-length SMN protein by 2-3 times essentially turning a
type I SMA infant (usually 2 copies of SMN2) with an 80% chance of dying or
going on permanent ventilation by 18 months into a much milder form of the
disease where patients have 4 or more copies of SMN2 and have an almost normal
life expectancy (note: those with 3 copies, usually type II SMA, live into
teens/early adulthood).

While as a
parent, I would almost do anything for my child to get access to the drug and I
do understand there to be calls for immediate (à once diagnosed, the window of
treatment opportunity may be quite narrow) regulatory action, the first
consequence of today’s data should be getting SMA on mandatory genetic panels for newborn screening. Only then
will there be maximal benefit once the ongoing blinded phase III study reads
out in late 2016/early 2017.

Wednesday, June 10, 2015

How times have changed. Four years ago, Alnylam found itself on the
receiving end of a trade secret lawsuit regarding the delivery technology du jour,
SNALP LNP then, in which it ended up paying near-bankrupt Tekmira ~$70M to settle the
allegations. As I opined back then, Alnylam seemingly used almost any means to get access to the know-how to make
SNALP LNP delivery work in primates in an effort to rid itself of the reliance
on Tekmira, the inventors.

An interesting aside
of this is that it appears, contrary to representations by Alnylam, that the
GalNAc-ESC technology were invented at Merck, not in-house at Alnylam.

The Complaint makes it clear that Alnylam feels threatened
by the technologically very direct competition.
In a way, Dicerna’s new strategy was to become Alnylam's clone. What could be worse, given the differences in the
RNAi trigger lengths (~19bp Tuschl-type siRNAs by Alnylam; 25/27 and longer Dicer-substrate
versions by Dicerna) and the apparent importance of stability/degradation in
GalNAc technology, there is the distinct possibility that Dicerna’s version,
everything else being equal, would outperform (or underperform) Alnylam’s.

In light of recent apparently rapid progress at Dicerna on
GalNAc technology and the timing of events, the idea that Dicerna may have
benefited from the GalNAc know-how of ex-Merck scientists does not seem
far-fetched.

It is unclear to me,
however, whether you can expect expert oligonucleotide chemists to suddenly
forget everything about their former job.

Alnylam obviously takes care of that problem by enforcing
harsh non-compete and pay-for-silence practices against their former employees,
meaning that if you are an RNAi scientist that job at Alnylam will be your last
RNAi job in the industry, period.

Looking forward, I predict that the outcome of the case will hinge less on
the physical documents that were alleged to have been ‘misappropriated’, but on
whether or not the ex-Merck scientists could have re-invented GalNAc-ESC based
on their skills and publicly available information (including from Alnylam) at
the time. If so, then Alnylam only has
Merck to blame that it does not force their employees to leave their profession
when they lay them off.

Thursday, June 4, 2015

As you will probably know already, Regulus Therapeutics surprised us this
week with the sudden departures of both their CEO and CSO. These two individuals also happened to be the
insiders selling major positions in the stock earlier this year just days ahead
of critical data to be released on their lead clinical candidate, RG-101 for
the treatment of HCV ('Reading the tea leaves on Regulus insider sales').

While this would be a good reason for what looks like a sacking of the company’s two key executives (especially since
the exodus came as a pair), for investors the all-important question is whether
it is also related to bad news that we do not know about yet. Most importantly, does this also have anything to do
with the failure to report the viral resistance analysis which had been promised
to us for the EASL meeting in April?

It is this analysis that will determine whether the miR-122
inhibitor can facilitate 4-week treatment regimens which must be the goal for
this asset. This is because RG-101 is
the only serious long-acting agent out there in the HCV drug development arena
and 4 weeks of oral, short-acting antivirals do not seem capable of getting rid
of the virus.

If there was no resistance to RG-101, based on the available
data RG-101 given on week 4 would add ~6 weeks to deep viral suppression to
the treatment regimen, in a way resembling a 10-week oral regimen which have much higher
odds of viral clearance.
If viral resistance (and not waning drug levels as I am assuming) played a role in the rebounds
seen in the single-dose study, then this would not necessarily be the
case. I say ‘not necessarily’ because
even then, the risk of developing viral resistance to RG-101 should be much lower when given in
combination with other agents as is the plan.

Take-home: I remain cautious (but not short any more)
prepared to take advantage of another bout of panic selling that could come
with the release of the resistance analysis.
The quality of the new leadership to lead the exciting microRNA platform
will also indicate whether Regulus can finally live up to its original promise.
Long-term, whether precipitated by the insider sales or not, the changes should be good as morale at the company from what I can tell had been low.

PS: in more positive news, Regulus Therapeutics today reported
that a first-in-man study with their second most advanced microRNA Therapeutic,
RG-012 for the kidney-related orphan disease Alport Syndrome, has begun dosing.

Wednesday, May 27, 2015

RXi
Pharmaceuticals today commenced a secondary offering setting it on course to raise ~$10M, enough to finance the company for another year while expanding its pipeline and technology. It could thus mark a new chapter in the
life of this company which had shoe-boxed itself into a single-product (RXI-109 for
dermal wound healing) company following a toxic 2012 financing that gave Tang
Capital Partners de facto control
over the company (pro tip: when you see the likes of Tang or Deerfield getting involved, it usually is not to the benefit of common stock holders).

The news this morning that the preferred stock overhang (àTang Capital Partners) had finally been cleared, then paved the way towards the financing (amount and pricing to be determined).

With RXI-109
winding its way through phase II studies, it became clear that RXi had to
open itself up to new opportunities enabled by its promising self-delivering
RNAi platform. The financing will initially
allow RXi to develop RXI-109 also for ocular (retinal and corneal) scarring-related
indications such as wet AMD and cataract surgery. First eye-related clinical trials with self-delivering
RNAi triggers are expected to commence later this year.

The eye is
an interesting application of sd-RNAi technology not only for the lucrative eye disease market (both genetic and age-related of considerable unmet medical need), but also
because they seem to be able to penetrate throughout the eye (see image) whereas in
the skin, distribution currently is limited to areas close to the injection
site barring new delivery breakthroughs (patches, creams and the like). In addition to cholesterol, it may also be
interesting to test other ligands such as Vitamin A and E for enhanced uptake
into certain ocular cell types.

Lots of unexplored potential

Beyond the
skin and eye, self-delivering RNAi strategies hold considerable promise for
other tissue targets, both by direct/local and systemic delivery. In terms of local delivery, I would be highly
interested in the biodistribution of intrathecally administered sd-RNAi triggers
in non-human primates. This is because
of their long phosphorothioated single-strand overhang and thus similarity to
phosphorothioate antisense oligonucleotides which are starting to show amazing
results in the clinic for CNS applications (watch
out for update on the infant ISIS-SMNRx study by Isis Pharmaceuticals).

In terms of systemic
delivery, sd-RNAi chemistry and structure may synergize well with
conjugate-RNAi approaches, both in their simple (--> Alnylam GalNAc-type) and more
refined form (--> Arrowhead DPC-type). Even without further modification, RXi-type
self-delivering RNAi has shown surprising knockdown efficacy in models of
pre-eclampsia as shown by respected UMass scientists Melissa Moore and Anastasia
Khvorova (formerly of RXi Pharmaceuticals).

If RXi can
get the backing from serious biotech investors and eventually a new management
fit to lead a modern biotechnology company, the current $16M market valuation (for RXI-109 in the clinic for dermal
scarring and soon in the eye; self-delivering platform potential; stake in
MirImmune) of the company could make it an irresistible investment
opportunity. If management, however,
continues to dig in their heels and refuses to listen to outside advice chances
are that the financial death spiral will continue.

Suspicious shorting into financing

It used to be common biotech practice that
investors-in-the-know were allowed to short into financing resting assured that
the offering will allow them to cover at a lower share price. It is therefore remarkable that in the days
and weeks before the financing, the short interest has sky-rocketed from
virtually none to around 10% of the float and possibly much more by now due to
the delays in reporting short interest.

Saturday, May 16, 2015

In honor of 25 years of aptamers, or better the SELEX
process which underlies the discovery of aptamers, I thought it might
be a good time to revisit aptamers for the delivery of RNAi Therapeutics.

Aptamers are nucleic acids that have been selected to
preferentially recognize a target, usually a protein, via their 3-dimensional
structure in analogy to how monoclonal antibodies recognize their targets. Aptamers are showing most promise in
therapeutic development for the targeting of extracellular proteins in the eye
for applications like wet AMD and diabetic macular edema (see Fovista from Ophthotech).

Its success for systemic applications has been much more
modest, however, with short circulation times and unexpected adverse events in a recent phase III study (likely due to the PEG portion of the aptamer drug) largely
accounting for it.

Aptamers have also been considered as cell-targeting agents
for RNAi Therapeutics. Early reports
suggested efficacy in HIV and cancer models.
Skepticism around the on-target mechanism in these examples was
considerable though largely due to questions around how they were supposed to
escape the endosomes.

I also fell into the camp of doubters (and still have some reservations), but have adjusted my
view to a more productive one after it became clear that IF you had highly productive endosomal uptake like
ASGPR/GalNAc and a highly stabilized RNAi trigger, gene silencing is possible
even without explicit endosomal release chemistry.

Time to try the next iteration: Aptamer-DPCs

As there may not be another ASGPR-type receptor in the body
and to compensate for lower drug exposure compared to the liver, in the quest
to make aptamer-delivered RNAi Therapeutics more robust, the new learnings of
RNAi trigger stability are probably best applied within the context of DPC
delivery technology by Arrowhead Research.

Accordingly, the perhaps 10x lower uptake in say PSMA-expressing
prostate cancer cells will be compensated by adding the RNAi trigger-aptamer
complex (as one or separately) to a masked endosomal release polymer. In case that the target cell receptor is only
abundant, but does not support productive endosomal uptake, another aptamer may
target a second co-receptor on the same cell (akin to some bispecific antibodies, co-receptors in viral cell uptake).

Following endosomal uptake, the masking groups come off,
endosomal permeability increased so that the RNAi trigger may escape into the
cytoplasm. In certain configurations, a
Dicer substract-type RNAi trigger structure may simplify design and increase
stability.

Tuesday, May 12, 2015

Dicerna Pharmaceuticals recent move from Watertown to
Cambridge is symbolic for its continued search for a place in the RNAi
Therapeutics landscape. Following some setbacks
in its cancer and home-brew LNP efforts, the company now pins its hope on that it
can compete head-on with Alnylam in the development of GalNAc-RNAi trigger
conjugates for gene knockdown in the liver.

Oncology on hold

Like others in the field, confidence in its cancer program
(DCR-MYC in phase I/II studies for solid cancers and HCC) seems to be low. In the absence of clear-cut early development-stage
cancer responses and confirmation of bona
fide tumor-wide gene knockdown, cancer drug development remains a
hit-and-usually-miss for the Oligonucleotide Therapeutics industry.

As a result, Dicerna seems to view their own mouse data with
skepticism just as I myself have yet to see data supporting tumor penetration
and bona fide knockdown in
well-controlled studies. The company has
to be credited that it is now setting the bar for DCR-MYC quite high when clinical
data from higher-dose cohorts is expected to emerge around year-end. If DCR-MYC does not make the cut, Dicerna
will likely cut its losses in cancer drug development and LNP research in
general.

DCR-PH1 close call

Dicerna management was also surprisingly frank about their
hesitations about the technical success of their most interesting current
program, namely DCR-PH1 for the treatment of hyperoxaluria type I.

After reviewing the latest non-human primate studies, it now
appears that at least an 85% mRNA knockdown of the HAO-1 target gene will be
required to see the key oxalate biomarkers ‘move’, and over 90% for more robust
movement. Based on rodent data, the
company had thought that 75% might be sufficient.

In NHP studies of DCR-PH1, an 84% average peak knockdown was
seen following a single dose of 0.3mg/kg of a Tekmira SNALP LNP formulation
with 68% knockdown remaining at week 4.
0.3mg/kg seems to be the current well-tolerated upper dose of Tekmira’s
LNP formulations and almost identical (protein) knockdowns were observed with 0.3mg/kg
of Tekmira LNP-formulated ALN-TTR02.

In clinical 3-weekly multi-dose studies of ALN-TTR02, this
translated into sustained 80-85% target gene knockdowns. This means that Dicerna now relies on the
safety of DCR-PH1 to allow for doses of around 0.5mg/kg. Not impossible, but probably a close call given the history of SNALP LNP and further exposes DCR-PH1 to competitive threats.

GalNAcs coming

Given the stage of their internal cancer and LNP efforts,
Dicerna is now pinning its hopes on taking on Alnylam with GalNAc-RNAi
trigger. This is where Dicerna is
currently investing most of its R&D efforts in.

It has now disclosed non-human primate data from those
efforts, with 5 consecutive daily doses of 2.5mg/kg GalNAc-Dicer substrates
resulting in ~70% knockdown of HAO-1 2-3 weeks after this loading dose. Given the larger molecular size of the
extended Dicer-substrates versus Tuschl-type siRNAs, this corresponds on a molar
basis to ~1.5mg/kg of Alnylam’s GalNAc-siRNAs.

This is somewhat less than what Alnylam presented for their PH1 program at OTS 2014 (ED80s in rodents of ~2.5mg/kg weekly) and Dicerna's GalNAcs would seem to require some further refinements to be competitive.

But in this case, they will end up with something that has little
pharmacological distinction, is 3-4 years behind Alnylam, which in turn is not
shy to put legal/IP pressure on its competition.

In my opinion, Dicerna
management and Board need to put in quality time to find their true identity.

Disclosure: I am short DRNA as a relative valuation short for my ARWR long position. DRNA has a slightly larger market cap than ARWR, but ARWR has a distinguished, more mature DPC pipeline with ARC-520 and ARC-AAT two attractive candidates in the clinic whereas DRNA has nothing in the clinic it apparently has confidence in. It's possible that both stocks are grossly undervalued, but relative valuation is one of my main RNAi investment methods and this is why I'm applying it here. Nothing personal.

Sunday, May 3, 2015

In late 2012, Arrowhead Research shocked the Oligonucleotide
Therapeutics world when it presented spectacularly potent and prolonged gene
knockdown data in non-human primates using a subcutaneously administered
single-molecule Dynamic Polymer Conjugate (DPC) formulation. This arguably represented the most elegant
delivery technology at the time.
Moreover, also due to its small, but not too small size (10-20nm) and
slight negative charge, it provided us with a glimpse into the future of systemic RNAi delivery for regulating genes beyond the liver.

It certainly got my
full attention and made me invest almost 100% of my stock portfolio back then.

Unfortunately, despite the validation in non-human primates
which suggested clinical readiness would not be far off, the subQ DPC technology
has seemingly struggled to reach clinical/commercial maturity. Not only
Arrowhead’s lead development candidate, ARC520 for HBV, but also its second development candidate,
ARC-AAT for AAT-related liver disease, was still based on the intravenously
administered two molecule DPC version.
Although the reasons for the delays were never really disclosed, a few
comments here and there made it seem very likely that chemistry and manufacturing
issues were behind the delay.

Back to the Future

Last week, Arrowhead Research finally published a paper
showing that single molecule DPC is still alive and kicking (Rozema et al.2015) and is progressing towards clinical application. In essence, the new single-molecule subQ DPC
prototype comprises of a membrane-active polymer which has been masked from
premature cytotoxic interactions by pegylation and cell-targeting ligands that
are added via protease-sensitive bonds;
as before, the highly modified/stabilized RNAi triggers are appended by
disulfide chemistry.

The DPC is made in a 4-step process followed by a
purification step to remove unwanted side-products and reactants. The latter step is apparently important when
going into primates.

The new old DPCs are thus distinguished from the intravenous
version not only in that it combines the RNAi trigger and endolysosomal release
polymer in a single molecule, but most importantly by the nature of its
triggered release mechanism. Whereas in
the former DPC generations triggered release was dependent on changes in pH such as they occur when a DPC is endosomally taken up, they are now responsive to the
presence of certain proteases in lysosomes.

pH-dependent formulations apparently suffered from instabilities
both in the body and during storage.
This was adequate for targeting genes in the liver because of the ready
access of macromolecules in the circulation to this organ following intravenous
administration, but not when the DPC first has to reach the circulation from
the subcutaneous space and when less well accessible target organs are the
ultimate destination.

Accordingly, non-liver single-molecule DPCs of the latest publication
had impressive circulation half-times of
the intact, protected molecule of 11 hours. Similarly, such DPCs are stable for at least a
year both in solution and when lyophilized.

The extra-hepatic
potential thus facilitated by increased stability now needs to be
demonstrated by finding suitable targeting ligands and I’m sure Arrowhead has
been busy working on that. It should be
noted that for target tissues where high concentrations comparable to the liver
are unlikely to be achieved following systemic delivery, the extra kick that
comes from an explicit release chemistry could provide a critical advantage
over competing approaches. These include
simple conjugates of the GalNAc-type and probably also self-delivering RNAi
trigger chemistries which incorporate ‘milder’ release chemistries (like lipid
tails).

Knockdown lasting for
weeks and months

The most impressive demonstration of the single molecule DPC
performance in the Rozema paper came from the primate studies. Here, a single administration of 0.5mg/kg 2’-O-methyl/F-modified
RNAi trigger led to a highly potent knockdown (peak knockdown >95%) of liver
expressed Factor VII with >80% knockdown of 2 and 4 months following
subcutaneous and intravenous administration, respectively.

Following the 2012 delays and some uncertainties around what
was really new and old in the recent publication, I am somewhat hesitant to declare that subQ DPC is now fully de-risked and ready-to-go.
In that regard, it would be helpful to learn more about the tox profile
of the new molecules and related to that which polymers will be eventually used
(e.g. 2-molecule with melittin-like peptide, a polyacrylate in the
publication).

Nevertheless, since Arrowhead has said that the new 2015
development candidate may be from the subQ line of DPCs (or if not going after
a extra-hepatic target) one would think that the most important challenges have
now been overcome.

Wednesday, April 29, 2015

Now that the HBV world has gathered extensive clinical experience with
interferons and polymerase inhibitors (NUCs) and with the resolve to finally find a
cure for a serious disease afflicting hundreds of millions worldwide, the
hepatitis B surface antigen (HBsAg) has become recognized as the key determinant for treatment
outcome. This is being confirmed by trial after trial investigating combining the actions of both NUCs and interferons,
either one after the other or together at once.

Some of these studies were presented at the International
Liver Congress last week in Vienna (ILC2015). Emerging from them are actionable HBsAg rules which
can predict fairly well whether a patient will eventually seroconvert to (or at least
lose) HBsAg. No matter the excitement around CRISPR technologies, HBsAg seroconversion remains the gold standard outcome in HBV treatment in the foreseeable future.

These rules can be divided into pre- and post-IFN treatment onset.

In the pre-IFN setting, it is
those patients that have below ~500 IU/ml serum
HBsAg as a result of NUC treatment that will most likely respond to interferon
treatment/immune stimulation with s-antigen seroconversion (see earlier blog entry). Since NUCs alone hardly do anything to
promote s-antigen seroconversion despite its dramatic lowering of viral HBV
titers, it appears to be their slow impact on HBsAg levels ( 0.1 log per year HBsAg reduction) that has the synergistic effect with interferon: with HBsAg
lowering you take off the foot on the immune brake, with interferon you step on
the immmune gas pedal.

As such, HBsAg knockdown by RNA(i) Therapeutics would seem
to do the same for interferons as NUCs do, only in a more rapid and potent
manner. Of course, both could be used
concurrently as a run-in to IFN treatment.

However, once on IFNs (post-IFN onset),
it is the relative HBsAg decline that has high
positive predictive value in prognosticating who will seroconvert. Of note, the HBsAg decline comes before any adaptive immunity can be
detected. This supports that HBsAg decline in itself contributes to seroconversion
rather than it being a mere correlation.
In that setting, it is a 1 logdecline
in HBsAg the first few weeks after IFN treatment onset that separates the winners
from the losers.

It is uncertain to me, however, whether 1 log is a precondition to s-antigen seroconversionas the non-responders do not
even come close to that (maybe 0.3log).
It is therefore possible that anything that pushes HBsAg below say -0.3-0.5log
could have a dramatic effect on s-antigen seroconversion rates.

An RNAi Therapeutic for HBV used simultaneously with IFNs may
therefore aim at helping IFNs to get to the
0.5-1log reduction threshold, and rapidly at that.

Ergo, there are now a number of obvious strategies that one
can apply regarding the use of RNAi Therapeutics in HBV with various knockdown goals,
both absolute and relative. The exact strategy would depend on how the RNA
agent is combined with polymerase inhibition/NUCs or immune
stimulation.

While a number of other HBV targets were reported at the
conference such as core assembly and entry inhibitors, HBsAg (and HBV mRNA
knockdown in general) lowering remains the most distinguished and the mechanism predicted to be most synergistic to existing treatment approaches. As combination treatment is strongly
predicted to be the future of HBV, HBsAg lowering should become a pillar of
those treatment regimes.

Monday, April 27, 2015

Having attended the International Liver Congress last week in
Vienna, Austria, it has become clear to me that HCV is not going away soon. Even in the US where progress towards its ‘eradication’
may be considered most advanced with about 1/5 of the known patient population
treated last year alone (~250k), it will be an uphill battle to identify, treat, and pay for the
millions more infected. Worse still, it is not enough to simply cure the existing pool of HCV patients, but also stop the cycle of re-infection (largely the result of injection drug
use).

Treatment cost is
one challenge and the current drug rationing approach leads to the
counterproductive warehousing phenomenon where current medical intervention is focused on
the patients with more advanced liver disease. This is not only the hardest-to-treat
population, but also allows the liver health of the previously less sick patients to deteriorate. This obviously makes little sense also from a pharmaco-economical perspective when getting rid of HCV early on has now been
shown over and over again to dramatically reduce HCV-related cirrhosis and
liver cancer.

Another problem is the fractured
treatment landscape that exists for the various patient populations
(split up according to fibrosis/cirrhosis stage, genotype, co-morbidities, the rapidly growing
concerns around drug-drug interactions, available/accessible meds etc) making
it difficult for even the learned gastroenterologist to keep up with the latest
developments and putting HCV treatment practically out-of-reach for the general
practicioner.

12-24 weeks
remains the standard drug treatment duration with docs worrying about shorter
treatment regimens being sub-optimal. A triple regimen by Gilead after 4 weeks of
treatment merely achieved a 27% SVR12 which in the DAA world is practically synonymous with a cure. The best shot at shortening treatment duration may therefore come from Achillion with 6 week of DAAs
achieving high cure rates in 'easy' patient populations.

While interferon is on the way out, it could make an at
least transient comeback for the hard-to-treat genotype 3 where, in addition to cirrhosis, cure rates with the all-oral DAAs low (60-80%).

To sum it up, the liver community has expressed multiple
times at ILC2015 that a short-acting pangenotypic regimen is an important goal
in the development of new medications for HCV.
And if they paid attention at the oral late-breaker on Saturday, RG-101
is poised to play a critical role in filling this unmet treatment goal due to its long duration of antiviral activity
following administration, regardless of genotype.

RG-101 update: more relapses, but thesis intact

The clinical investigators of Regulus Therapeutics presented
a 20 week update on the phase I study in genotype 1, 3, and 4 patients with good
to moderate liver health. 28 patients
received study drug RG-101, 4 placebo.

At the primary endpoint on week 8 (reported in earlyFebruary), slightly more than half (15/28) of patients treated with RG-101 were
below the level of quantitation (BLOQ).
According to the company, most of them were not only BLOQ, but undetectable (by sensitive PCR) at that. This is a remarkable feat given that the
GalNAc-conjugated phosphorothioate antisense molecule had been only given once.

According to the latest update, half of those patients
eventually relapsed (7-8 depending on
whether you count the patient that was lost to follow-up), most of them
shortly after week 8. Although the
relapsers are slightly disappointing as in the short-acting DAA world
undetectable virus for 8 (or better 12, SVR12) weeks following cessation of treatment
is more or less equivalent to a full-blown cure.

Of course, the prognostic rules for a long-acting agent like
RG-101 with a slower onset of antiviral knockdown ought to be different. The notion that the viral rebounds were
simply due to waning drug levels in the liver (and not due to viral escape mutations!), was supported by the
biomarker analysis in the healthy volunteer part of the phase I study, also presented
at ILC2015, where the trough in viral knockdown (~day 28) more or less
coincided with maximal total cholesterol lowering as a predicted by miR-122
biology.

Of note, there was no apparent benefit of increasing the
dose from 2 to 4mg/kg which was consistent with preclinical evidence that
showed a declining liver/kidney drug ratio at 4mg/kg and maximal cholesterol
lowering at 2mg/kg in humans. This indicates that ASGPR receptor binding becomes
saturated when too much GalNAc antisense is given at once. The increased drug liver concentration at
higher concentrations observed in earlier preclinical studies probably indicate
uptake in non-productive compartments of the liver, including Kupffer and sinusoidal
endothelial cells.

The hope is that with a second dose of RG-101 28 days after
the first shot, maximal viral suppression can be maintained for at least another 4
weeks to stave off any viral comeback as seen in the single-dose study.
This is supported by both the healthy volunteer part of the study and
the chimeric PXB mouse experiments presented which showed that such a second
dose not only maintained drug potency, but in fact led to a step-up in efficacy. I am therefore optimistic that with 2 doses
of RG-101 monotherapy alone ~50% cure rates can be achieved in patient
populations similar to that in the phase I study.

This, however, is not even the goal. The ultimate goal
would be to establish a simple pan-genotypic 4-week treatment regimen. Accordingly, the combination of RG-101 with a
DAA(s) (sandwich regimen) can be expected to result in a very, very deep viral knockdown by week 4.
At this point, a second shot of RG-101 would be administered to give the
immune system another 6 weeks or so to finish off the virus. I believe a very realistic scenario, and
depending on which patient populations you are looking at a very compelling
alternative to current HCV medications and those in development.

PS: Open questions

Unfortunately, given that cholesterol lowering was still
close to maximal at week 8, it would have been comforting to show a mutation
analysis from the clinical study to confirm that viral relapse was not explained by the virus successfully developing resistance against RG-101. This is such an obvious question that one
wonders why Regulus did not present the data (yet).

Another question mark around the current data set is why Regulus is not disclosing the
differential effect of RG-101 on good and bad cholesterol and instead is reporting total cholesterol lowering. The study investigator said that they are still analyzing the data from the multi-dose healthy volunteer study (months after completing dosing???) and are planning to publish those. I am
mildly optimistic that this could unexpectedly bring to the fore the cardiovascular potential of
miR-122 targeting, although in this case (à mostly chronic treatments)
the liver cancer concern around miR-122 inhibition may be more valid than it is
for the 2-shot HCV treatment goal.

Thursday, April 23, 2015

I just walked into an early morning session at the International
Liver Congress in Vienna and may have learned the most important nugget of
information regarding RNAi treatment for HBV.

During the discussion in the ‘Banishing B’ session, Dr.
Joerg Petersen referred to clinical analyses to be presented this Saturday
showing that patients who achieve HBsAg levels of less than 500, or even better 200 IU/ml and then
are given an interferon have a much better chance of eventually losing HBsAg,
i.e. being functionally cured, than those that do not.

Dr. Petersen has been involved in clinical studies combining
nukes and an interferon, and data presented at last year’s American Liver
meeting (AASLD) showed that 9% treated with the combination for 1 year lost HBsAg in the
year following combination therapy compared to just 2.8% receiving interferon
alone.

Note that currently only interferons are thought to give you
a chance of functionally curing HBV by medication and that HBsAg seroconversion
attributed to interferon treatment may occur in the years after cessation of
interferon therapy. It will therefore be
important to see whether this increase in seroconversion with combination
treatment continues to hold up in subsequent years. The nukes are ‘only’
thought to protect the liver from the ongoing damage from HBV replication and may
have to be given indefinitely.

I am not sure whether the new insight comes from a fresh
clinical study or are the result of a more detailed subgroup analysis of the
previous study. Regardless, it hammers
home a message that can be heard again and again, even more so in Vienna this year than
at the London meeting last year: it is all
about HBsAg lowering.

Implications for HBV
RNAi

The implications of the new analysis for RNAi approaches for
the treatment of HBV is obvious: use RNAi to get HBsAg below the
threshold. In other words, it may be less
about getting a magical 1log knockdown, but more about getting patients below 500IU/ml.

For this, Dr. Petersen recommended using 2 nukes so that the
tiny and very slow HBsAg declines observed on nukes continue ( < 0.1 log per year). With
RNAi agents, you would likely achieve this goal for a patient with an HBsAg at
baseline of 1000IU/ml within a month, even with a single 2mg/kg dose of ARC520
from Arrowhead Research as reported last year.

The absolute knockdown potency of an RNAi agent would
determine which fraction of the HBV population fall within this sweet spot.
With a 1log knockdown e.g. you could start RNAi with patients with as much as
5000IU/ml.

For the clinical development of RNAi agents for HBV, the
first step will be to determine the HBsAg decline on a background of
nukes (just what Arrowhead is doing right now). For pivotal trials, an
immunostimulatory agent such as an interferon should be added to the nukeà RNAi/nuke treatment
regimen to finish off the virus.

Stay tuned to learn about the fold benefit of HBV cures in
patients falling below the 500IU/ml threshold, and the 3-4mg/kg single-dose
results for ARC520 from Arrowhead Research to be reported later this quarter (note to Arrowhead PR department: next Monday may be a good time to do so).

Wednesday, April 22, 2015

ALN-TTR02 for the treatment of
TTR amyloidosis is the most advanced RNAi Therapeutic in clinical development
and has been carrying the torch for the field as whole. Expectations are therefore high and a
stumble in this program as a result of the therapeutic hypothesis underlying
the program not panning out would likely trigger a temporary*, but steep
sector-wide sell-off.

* it should be
clear, however, that with the current ability to robustly knock down genes in
the liver, RNAi Therapeutics will result in a number of successful treatments.

It therefore came as a relief yesterday when Alnylam presented (press release here, data slides here) 12-month data from an open-label
extension phase II study of ALN-TTR02 in the polyneuropathy form of the disease
(FAP) showing

a)continued
robust gene knockdowns for more than a year (88-80% reductions peak/trough in
3-week cycle);

b)disease stabilization (if not improvement) when the
Natural History of the disease would have predicted marked deterioration (predicted mNIS+7 at 12 months of +18 in
Natural History vs ~-2.5 on ALN-TTR02).

Furthermore, the safety of this liposomal formulation enabled by Tekmira seemed more than
sufficient for a disease as severe as FAP TTR amyloidosis (5-15 year survival
following diagnosis) with the most significant adverse events being related to the intravenous
route of administration meaning that ALN-TTR02 should be given under trained medical surveillance.

There are some questions that
remain open, some of which should be answered by the ongoing phase III APOLLO study which should
complete sometime in 2016 (with an 18 month primary endpoint).

Firstly, it will be important to
show disease stabilization to be strictly related to ALN-TTR02. In the phase II study, most patients (20 of
27) were on tetramer stabilizers which have previously shown to result in very
modest (tafamidis) to moderate (diflusinal) therapeutic benefits. While neither tafamidis nor diflusinal have
shown disease stabilization after 12 months, the concern remains that they
could have contributed to the apparent therapeutic benefit seen in the phase II
study.

To my surprise, the 7 patients
not taking tetramer stabilizers on top of ALN-TTR02 seemed to do even better, at least numerically than those taking them (-6.5+/-9.2 vs -1.1+/2.5). Although the number was quite small, the fact
that this is the opposite result from what one might have expected, it is possible that a slight placebo effect may have played a role in this open-label study:
those for which ALN-TTR02 was the only medical intervention might have had a
greater ALN-TTR02-driven placebo effect.

Other more complicated explanations based on TTR lowering affecting the PK/PD relationship of tetramer stabilizers are also possible if this phenomenon is for real.

Fortunately, the blinded phase
III APOLLO study will compare ALN-TTR02 to patients taking no tetramer stabilizers to treat their FAP. Finally, it
would be of interest to look at the effect of ALN-TTR02 on the spleen in the
APOLLO study as spleen toxicity due to lipid stability might be the most
important safety parameter with chronic dosing.

In summary, yesterday’s 12-month
data removed important overhangs over the RNAi sector and we are on track for
the first commercial RNAi drug in 2017. Seeing
is believing.

Sunday, April 19, 2015

If you are involved in cancer drug development, you are probably thinking of ways to exploit checkpoint inhibitors for your
purposes. Checkpoints are the mechanisms
whereby cancer cells avoid being recognized by the immune system as foreign and
the initial clinical results of inhibiting them, e.g. by targeting CTLA4 and PD-1/PD-L1, has caused immune-oncology as
a whole to take the cancer drug development space by storm.

Suddenly, every scientist and their technician believe that
by taking checkpoints out of the equation, their immune approach to cancer,
which in many cases was marked by failure after failure in the past, will
work.

Take e.g. cancer vaccines and the idea of grinding up tumors
and use the cell mash to train dendritic cells.
Sounds compelling to me, but I also know that I lost a bunch much money on
the very same idea 10 or so years ago with nothing, but some early promising
data from the clinical Wild East to support it.

Others meanwhile believe that their technologies may enable immune-oncology by e.g. being able to modulate the tumor
microenvironment so as to permit better access of the tumor killing cells.

RNA Therapeutics are
no exception. RNA Therapeutics, due
to its endless targeting opportunities, has always been considered promising
for oncology, but has struggled to show clear-cut success either due to drug
delivery issues or due to the difficulties of predicting immune activities based
on rodent studies.

Emblematic of this reversal of fortunes is the toll-like receptor (TLR) field of
activating the innate immune system with oligonucleotide stimulants. The idea here is to provide an environment
that is more conducive to tumor cell killing and/or to directly impact tumor
cell survival (e.g. interferon stimulation).
Art Krieg, of TLR9 (CpG) fame, but who has been erring as its lost son
in the (blooming) deserts of RNAi, RNaseH antisense, splice modulation, and RNA
activation, is apparently re-energized enough to go back to TLR Therapeutics and has started Checkmate
Pharmaceuticals which will likely try and harness
TLR agonists for cancer immunotherapy.

Nanoparticle delivery
may also see a revival. This is because
they have a propensity, usually undesired, to be taken up by phagocytic cells,
some of which may be effective in antigen presentation (e.g. dendritic cells). I have thus noticed that a number of mRNA cancer vaccine approaches involve
nanoparticle delivery with the aim of expressing tumor antigens in the training camps
of the immune system, the lymph nodes.

Nanoparticles may also be a way to knock down the gate-keepers in the
tumor microenvironment which inhibit tumor infiltration by cytotoxic T (incl. CAR T-cells) and other helpful immune cells. Since
gate-keepers should be most useful when positioned at the entrance, this might actually take
advantage of another limitation of many nanoparticle delivery technologies, namely
getting stuck close to the vasculature instead of penetrating deep into the
tumor.

Once deeper into the tumor, the struggle may not be over for
cytotoxic T cells and tumor eating cells due to potentially immunosuppressive activities
in the tumor microenvironment. This is
the new positioning for the phosphorothioate-based
antisense molecule ISIS-STAT3 by
Isis Pharmaceuticals and AstraZeneca for which, like for other
phosphorothioate-based approaches, the demonstration of robust uptake and gene
knockdown activity in tumor cells themselves is lacking, but functional uptake
in cells of the tumor microenvironment has been reported.

Finally, RNA Therapeutics such as CRISPR genome editing or
straightforward self-delivering RNAi
(see recent license of MirImmune from RXi Pharmaceuticals) can be tools for the
ex vivo preparation of T- and
dendritic cells. A self-delivering
approach may be advantageous here as it may function in normal cell culture
media and thus not confound cell signaling pathways in the maturation of these cells.

Investor, tread carefully

Overall, I’m convinced that there are synergistic potentials
to be exploited and checkpoint inhibition may open the door to certain that have failed in the past.
Nevertheless, one should be mindful that most immune oncology drugs only work in a fraction (maybe 25%) of patients and the current hype around immune oncology guarantees that
there will be many bad apples for investors to avoid. Trust me, I've seen it when RNAi was indiscrimately hyped and abused for short-term financial gain in 2006-8. Just because you can contrive a link to
immune oncology or because a desperate Big Pharma does a deal, does not mean that all the biological problems will dissolve. The bubble will burst after which mostly only well-financed quality
plays will recover.

Disclosure: I am fishing for short opportunities in the immune oncology space as a hedge against a (hopefully temporary) correction to what seems to be an in a number of areas (e.g. gene therapies, immune oncology, one-drug orphan wonders such as Alexion etc) overheated biotech space.

Wednesday, April 8, 2015

When it is screaming into your face that your business model
has failed you and the young competition is running circles around you, only then you
might be compelled to change.

This certainly is true for Big Pharma which have lost sight
that their business is to make a buck while increasing the health of their
customers instead of wasting time and energy on challenges like turning a twice-a-pill into a once daily therapy. In its quest to optimize
their business processes, it has thus thrown out of the window revolutionary, innovative
technologies that just would not fit into those loved models.

Case in point, Merck writing off their multi-billion dollar investment in RNAi Therapeutics and selling it to Alnylam for $175 in largely equity and some cash. Alnylam then turned
around and made at least a 10x return on the RNAi trigger stabilization
chemistry by Merck in little more than a year.

This is a rough estimation of how much the
Merck RNAi assets have approximately contributed to increasing Alnylam’s market cap.

AstraZeneca leading the way for Big Pharma in RNA
Therapeutics

Not long ago, AstraZeneca was widely vilified for being the worst
of the worst in terms of R&D productivity.
Their labs just would not produce new compounds that mattered to
patients.

After a corporate shake-up, things certainly have changed on
the innovation front. AstraZeneca has
fully emerged as a real risk-taker when it paid Moderna $240M in upfront monies
alone for access to a comparatively early-stage mRNA Therapeutics platform in 2013.

Before that, however, it already got active in the RNA
Therapeutics in a less visible manner, notably with a much smaller, but possibly more profitable
deal with microRNA Therapeutics platform company Regulus Therapeutics.

In the 2012 deal, AstraZeneca made a $25M equity investment in addition to a token $3M cash hand-out in the then privately-held Regulus Therapeutics. In exchange, AstraZeneca received 3
microRNA target picks in the cardiovascular, metabolic, and/or oncology areas.

The best part of the deal for AstraZeneca (and the reason why I took money
off the table today at what I considered an outsized reaction) was that it only has to pay $2.5M per target/candidate pick and Regulus Therapeutics
has to pay for part of the work involved in generating the candidate at that. There would, of course, be the milestones and royalties, but they should also be modest, in-line with the $2.5M payment due now.

Oh, those were the good old times of abusive (because they could) Big Pharma biotech
business development deal right on par with the steal that The Medicines Company got
from Alnylam with regard to the PCSK9 target.

But still, you have got to credit AstraZeneca that unlike
its brethren they not only sealed the deal, but actually advanced one of the
first clinical candidates involving a fundamentally new molecular target
class. It will be interesting whether
they will do the same in mRNA Therapeutics.

Anti-miR103/107 antagonism for improving liver health in
diabetes

Initially, the focus of the partnership had been on what looked like a very promising HDL-augmentation strategy by inhibiting miR33 in the
liver, but this candidate has apparently taken a backseat in favor of the insulin-sensitizing
strategy by inhibiting miR103/107.

It had been known that in type II diabetes, there is an inverse correlation between insulin sensitivity and miR103/107
expression. Supporting a causal
involvement, inhibiting miR103/107 in mouse models of diabetes with
(unconjugated) antisense oligonucleotides increased not only insulin
sensitivity, but also had positive effects on a couple of other diabetes-related
parameters not only in the liver (e.g. triglyceride levels), but also body fat
(adipocyte size/differentiation).

One puzzling aspect, somewhat akin to Regulus’ Alport’s program (--> miR-21),
in exploiting anti-miR103/107 for pharmacological intervention is that it was initially uncertain what the
target cells ought to be: adipocytes and/or hepatocytes? A role for miR103/107 expression in adipocytes
was particularly supported by the observation that its steady-state level there is
higher than in the liver and the fact that single-strand phosphorothioate
oligonucleotides also distribute to body fat.

However, with the adoption of GalNAc conjugation technology where most of the oligonucleotides now accumulate in hepatocytes it seems that AstraZeneca and Regulus have come to the conclusion that it is
the liver that once again is calling the shots here as it usually does in
diabetes. You can deduce this from the
fact that a GalNAc version was selected as the clinical candidate (AZD4076)
slated to enter the clinic later this year.

Taking advantage of the observation that anti-miR103/107 has positive effects on liver triglyceride levels, the clinical development of AZD4076 will at least initially be geared towards treating non-alcoholic steatohepatitis (NASH) in diabetes patients.

Tuesday, April 7, 2015

Benitec announced today that almost 1 ½ years after filing an IND for its DNA-directed RNAi HCV candidate, it has now obtained liver
biopsy data from first 3 of the 4 patients dosed so far. Needless to say, the analysis was a
resounding success confirming that the right AAV vector coding for the shRNAs
against HCV was administered to the trial subjects.

Given that no details were provided on the methods, I assume
that the evidence is based on PCR analysis which pretty much picks up almost any activity.

TT-034 also shined on safety with ‘no treatment-related serious adverse effects
(SAEs) in any of the four patients dosed’.

To wit, the motivation behind the gene therapy ddRNAi HCV
trial is to provide a one-shot cure from HCV infection.
The company, however, said that ‘the
amount of shRNA produced will not result in reduction of hepatitis C viral load’.

So while this statement almost makes it sound like they did
not look for antiviral efficacy, but that there might well have been, we can safely
assume that they did (standard blood test to look for HCV; plus RNA analysis from biopsies) and
failed to see such.

It is also curious
that no results from PCR-based target mRNA cleavage assays were disclosed
which, while still PCR, requires a certain amount of RNAi robustness to detect
with confidence and would have been used to further tout trial success.

At this point, Benitec has almost completed the first 2 of 5
planned dose cohorts. According to my
notes, the top dose is about 25x higher than dose group 2. To get from no change in viral titer to
undetectable while increasing dose by 25x seems quite optimistic to me. And even if this highly unlikely scenario materialized, at this pace, it will be sometime in 2023-4 when it would even be considered for approval.

So please, Benitec, if you cannot see a
knockdown at the next higher dose cohort, give it a rest.

Friday, April 3, 2015

This week, Dyax released early, but arguably impressive data from a
phase Ib trial of monoclonal antibody DX-2930 for the prophylaxis of Hereditary
Angioedema (HAE), a rare disease (incidence of 1 in 10-50k births) with a
rapidly evolving and growing market. The
results confirm that plasma kallikrein and, by extension, its precursor
prekallikrein (PKK), are highly effective and safe targets for the treatment of
HAE.

Due to the expression of kallikrein and other pathway components in the liver, HAE therefore shapes
up as yet another high-value indication after PCSK9/cardiovascular disease and CC5/complement disorders PNH and aHUS (à
Soliris) where RNA Therapeutics will be directly pitted against monoclonal
antibodies to answer the following pharmasophical question:

What would you prefer? Turn off the gene underlying a disease with a defined, synthetic molecule harnessing an endogenous biological mechanism, or mop up the disease-mediating gene product (protein) with a gemisch of cell-derived proteins?

You may know my preference already, and indeed, a phase I study of ISIS-PKKRx by Isis
Pharmaceuticals targeting PKK has just been completed and showed a 80-90% gene
knockdown at 300-400mg weekly subcutaneous injections.

Disease pathway: promoters and inhibitors

HAE is caused by the genetic absence or insufficient activity of C1 esterase
inhibitor (C1-INH). This predisposes to regular, often weekly to monthly episodes of tissue swelling which when abdominal can cause severe pain and when affecting the throat is life-threatening.

Although C1-INH is involved in a few intersecting pathways
such as coagulation and complement, the results by Dyax confirm the growing evidence that in the end it is all about plasma kallikrein and
subsequent vasoactive bradykinin generation. The
preclinical evidence includes an elegant study by Isis Pharmaceuticals (Bhattacharjee et al 2013) where the power
of RNA Therapeutics was harnessed to knockdown a number of players in the coagulation and kinin-kallikrein pathways to show that only inhibition of members of the
kinin-kallikrein pathway (e.g. PKK and factor 12) could reverse the symptoms caused by C1-INH deficiency.

Importantly, human genetics show that PKK deficiency is
without apparent medical adverse consequence, thus making it a drug developer’s
dream.

Therefore, although HAE is caused by a protein deficiency, a
therapeutic knockdown approach is conceivable due to the presence of promoters
and inhibitors in the pathway of disease. This is thus similar to antithrombin
and hemophilia for which Alnylam is currently advancing a promising RNAi Therapeutics clinical
candidate (ALN-AT3).

Poor pharmacokinetics of approved drugs leaves large
unmet need

There are a handful of drugs approved for HAE. Most of these are approved only for the mitigation
of an acute HAE attack. They have shown
modest efficacy with kallikrein inhibitor Ecallantide/KALBITOR
(a small protein by Dyax) and C1-INH protein replacement therapeutic CINRYZE (by Shire) approximately halving the severity of an attack or attack frequency, respectively.

In addition to some potentially severe side effects like
anaphylaxis (KALBITOR) and infusion reactions (CINRYZE), it is the poor
pharmacokinetics necessitating frequent administration that render them impractical for prophylactic use.

For example, CINRYZE, the only agent approved for prophylactic use, has to be intravenously infused twice a week (and some investors/companies moan when Tekmira's RNAi LNP products have to be infused every 3-4 weeks), and still attack rates
were reduced by only about a half. This
supports that despite frequent i.v. infusions, C1-INH levels cannot be kept
above the needed threshold for long enough.

Given that once set in motion, the swelling cascade is
probably difficult to stop cold, it is, however, chronic prophyxis that has the prospect of bringing most benefit to patients, in
addition to filling the coffers of biotech companies and their investors (prophylactic CINRYZE:
$300k per year).

DX2930 shaping up to be first satisfactory treatment

In light of the above, it is apparent that new drugs for HAE
should have both increased potency and be sufficiently convenient for chronic prophylactic
use. In terms of dosing frequency, this
means at a minimum once-a-quarter intravenous infusions, weekly subcutaneous
injections, or daily oral pills.

As a subcutaneously administered antibody, DX-2930, of course, almost naturally satisfies the dosing frequency requirement. Moreover, when 2 doses were given 14 days
apart, the attack frequency for the 300 and 400mg cohorts dropped by ~10x from
baseline during the time when plasma concentrations of the antibody were deemed
above the threshold needed to keep the kinin-kallikrein pathway in check (~6
weeks after 2nd dose). 13/15
patients (87%) were thus attack free from days 8-50 compared to only 3/11 (27%)
in the placebo group.

Attack frequencies for the 30mg and 100mg cohorts were not
reported. This probably means that these were not successful and support the
notion that whether an attack can occur or not is a rather sharp threshold
effect. Also consistent with this was
the fact that the 300mg cohort numerically performed better than the 400mg cohort in this small sample size.

[correction] Attack frequencies for the 30 and 100mg cohorts were also dramatically reduced from days 8-50 although these doses had been predicted by Dyax to yield suboptimal plasma antibody levels, possibly raising questions about the patient population chosen.

Nevertheless, DX-2930 appears overall very promising and has further
validated kallikrein/PKK as targets, but larger patient numbers are required to
determine the more precise efficacy benefit over existing drugs, the dose response relationshipo, and, of course,
safety.

RNA Therapeutics closing in

In addition to 2nd generation RNaseH antisense
compound ISIS-PKKRx, I expect a number of additional RNA Therapeutics
candidates to join the HAE fray due to the attractive economics of the market and the anticipated
high rate of development success. The
latter is largely a function of the validated nature of the kinin-kallikrein
pathway.

Although the DX-2930 study validates kallikrein, it should be cautioned that RNA Therapeutics cannot actually target kallikrein directly, but
merely its precursor, PKK, as kallikrein is generated from PKK by enzymatic
processing. This means that the
therapeutic threshold in terms of percent inhibition will be shifted either to
the left or right depending on the enzymology of PKK processing.

In summary, HAE and the kinin-kallikrein pathway should be one to put on your RNA Therapeutics radar, also because it may offer new avenues towards important large markets such as diabetic macular edema and inflammatory bowel diseases.

Friday, March 27, 2015

When Biomarin late last year bought Prosensa for its experimental
exon skipper drisapersen for the treatment of Duchenne Muscular Dystrophy (for $680M plus potential milestones), it
exuded confidence about the likelihood of getting approval for the 2’-O-methyl
phosphorothioate antisense molecule.
This, despite of the fact that drisapersen failed in a pivotal phase III trial of
186 patients which prompted the old partner GSK to dump the drug and walk away.

Tenuous early evidence for drisapersen in earlier trials

The confidence is largely based on some supposedly successful earlier
trials, especially a multi-center, randomized, blinded 53-patient phase II
study which had seen improvements in the 6 minute walk distance (6MWD) at week
25, the primary endpoint of the study (Voit et al. 2014).

This, however was statistically significant only the case in the subgroup of patients that received drisapersen continuously (à
treatment in 10 out of 10 weeks with 6mg/kg),
but not in patients which were treated identically, except for the small
difference in skipping the last week in a 10-week treatment cycle.

At week 49, the difference with placebo failed to
reach statistical significance and Prosensa had to resort to pooling both
subgroups to claim victory for that time point. Similarly, drisapersen failed in obtaining
statistically significant outcomes for other muscle function endpoints.

Since the mechanism of action for the DMD exon skipping
candidates is to change splicing of the mutated dystrophin transcript to a form in which the reading frame is restored with recovery of partial activity, it is important
to understand the relationship between drug treatment and dystrophin production.

Here, too, the evidence was less than robust. For example, even when applying the sensitive
immunofluorescence technique, no increase or even a decrease in dystrophin was seen in almost half of treated subjects.
With the less sensitive Western blot, an increase in dystrophin was seen in only a
third of treated subjects (0 for placebo).

Therefore, given the failed phase III trial and the less than robust earlier evidence in
favor of the drug, I struggle to understand Biomarin’s confidence in obtaining approval in 2016.

The importance of dystrophin as a surrogate endpoint

Part of the difficulty of obtaining statistically
significant results for muscle function endpoints is most likely due to the
small patient size (orphan disease affecting ~1 in 3500 male births) and the
consequent need to pool boys at various stages of the disease together in a given trial. It would thus not be surprising if say obtaining 10%
levels of normal or Becker-type dystrophin will translate into very meaningful
clinical benefit in some, but not other boys.

This will be an even more challenging problem for the DMD
subgroups that are not amenable to exon 51-based exon skipping which is
targeted by drisapersen. Probably
insurmountable for first-generation chemistries like drisapersen.

Accordingly, in both the drisapersen
and the competitive PMO-based eteplirsen trials, it
has not been possible to correlate dystrophin production with functional
outcomes.

For that reason, I strongly support the importance of
establishing reliable, quantitative methods to measure dystrophin in clinical
trials (there was an FDA workshop related to this last week). Dystrophin-dependent markers may
also be acceptable if they can be measured by means that do not involve taking painful muscle biopsies. For example, serum-based
microRNAs as developed by Rosetta Genomics and Marina Biotech would be of
interest here.

Eteplirsen before drisapersen

I thus find it difficult to grasp the notion of rejecting the current crop of exon
skippers like drisapersen or eteplirsen should they be found to produce
functional dystrophin with few side effects.
After all, it is the loss of dystrophin function that causes Duchenne
Muscular Dystrophy and one has to wonder how generating additional dystrophin
cannot be beneficial to patients, especially since the principle behind
drisapersen and eteplirsen is strongly supported by human genetic evidence (à Becker’s Muscular Dystrophy).

In this world, it has got to be eteplirsen that should
be first in line for regulatory approval.
This is because there is overwhelming evidence (e.g. Heemskerk et al., 2009; Sarepta's Barclays presentation March 12, 2015) that the PMO-based drug
is much more potent than drisapersen which, let’s face it, is based on
stone-age antisense chemistry (2’-O-methyl phosphorothioate). Such chemistry is characterized by
minimal efficacy and dose-limiting toxicities, especially renal in the case of
drisapersen.

In a paper comparing 2’-O-methyl to PMO chemistry for DMD
exon skipping conducted by researchers close to eteplirsen, it was found that
at same doses in mice, PMO chemistry is moderately to vastly more potent than 2’-O-methyl phosphorothioate antisense compounds of a size comparable to
drisapersen. The extent of the difference depended on whether the human or mouse dystrophin were targeted and the target sequence. Unsurprisingly given the acrimonious competition between the two parties, Sarepta has also picked up
on this and continued along these lines by showing that in addition to chemistry, eteplirsen has the edge over drisapersen in terms of the targeted sequence:

Sure, there is the theoretical caveat that PMO and 2’-O-methyl
scale differently from mice to humans and that what is the most potent target
sequence for one chemistry does not necessarily have to be the most potent one for
the other. Intuitively, however, the
differences are too big for these factors to compensate the preclinical
evidence. Also, keep in mind that in the
clinic, eteplirsen is being given at 5 to almost 10-fold increased doses than drisapersen
and, on top of that, is much safer and better tolerated than drisapersen.

Because of this and the competition, it is not surprising and disingenuous when Biomarin would now suddenly like to de-emphasize the importance of dystrophin as a surrogate biomarker (see last week's workshop).

Dear regulatory agency,
if you approve drisapersen, you cannot deny eteplirsen. Sure, drisapersen has been tested in more patients than eteplirsen and Sarepta has conducted a clinical
trial in the worst possible manner and probably ‘embellished’/overstated some of their results, including
the dystrophin evidence. However, given
that eteplirsen almost certainly generates more dystrophin than drisapersen,
the highly favorable side effect profile of eteplirsen (also in comparison to
drisapersen), and in light of the 6MWD issue that applies to both drug
candidates, the question is whether the bureaucratic application of rules
should trump scientific evidence and patient interests.

Disclosure: I am long SRPT based on the notion that Biomarin, with its orphan disease savvy, will turn out to be the biggest supporter of eteplirsen getting approval this time around. Additionally, the agency is partly responsible for the long duration of the ongoing eteplirsen trial (close to 4 years soon) and the repeated taking of muscle biopsies, and after all this taking away hope from patients and their close ones is difficult to fathom.

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